Copper alloys are uses as the base materials of electric and electronic components such as connectors and terminals applied generally to automobiles, household electric appliances, office automation equipment, and the like. These base materials are treated by plating in order to improve the functions such as rust-prevention, improved corrosion resistance, and improved electric characteristics. Specifically a tin-lead alloy plating containing 5 to 40% by weight of lead has been widely used owing to excellent anti-whisker performance, solder wettability, adhesion, bendability, heat-resistance, and the like, (for example, refer to Japanese Patent Laid-Open No. 8-176883 (PTL 1)).
In recent years, however, the influence of lead on the environment drew attention, thus there has been rapidly progressing the switching to a plating not containing lead, or to a lead-free plating, as a measure for environmental conservation.
On the other hand, the lead-free tin-containing alloy plating likely generates whiskers on the surface of plating. Consequently, accompanied with the densification of electronic components in recent years, the tin-containing alloy plated products raise serious problems such as the generation of whiskers, the contact resistance failure caused by surface oxidation, and the electric short circuit.
Responding to these problems, persons skilled in the art studied the anti-whisker measures on the tin-containing alloy plated products. Japanese Patent Laid-Open No. 2008-88477 proposed a method forming specific base layer and intermediate layer, applying tin plating, and further conducting reflow treatment, (refer to PTL 2). Japanese Patent Laid-Open No. 2008-194689 proposed a method forming two kinds of tin plating films each having different crystal types, thus suppressing the generation of whiskers, (refer to PTL 3). Furthermore, Japanese Patent Laid-Open No. 2008-280559 suppresses the generation of whiskers by treating connectors and the like, on which lead-free tin-containing alloy plating is applied, with ultrasonic waves, (refer to PTL 4). These methods have, however, complex process compared with the cases using tin-lead alloy plating.